A pale orange-brown marmoset very similar to M. humeralifer obtained from the Rio Arapiuns in the northern part of the range was photographed by Mittermeier et al. (1988, p.20) in the collection of the Belém Primate Centre. It is believed that this was a chromogenic anomaly.

Field research since the publications of Hershkovitz (1977) and Rylands et al. (1993) has diminished the supposed distribution of the Santarém marmoset. Hershkovitz’s (1977) range is now divided into four, being occupied by marmosets now considered distinct species: M. mauesi, M. saterei and M. acariensis besides M. humeralifer. According to our current understanding, M. humeralifer occurs south of the Rio Amazonas, between the Rio Maués (and possibly its tributary the Rio Parauari) in the west, and the Rio Tapajós in the east. The southern limit is not known, but may be in the region of the Rio Paracari. The southernmost locality for the Santarém marmoset plotted by Hershkovitz (1977) was Vila Braga, 4º25'S, on the Transamazon highway, just north of the Amazonia National Park.

Marmosets and tamarins are distinguished from the other monkeys of the New World by their small size, modified claws rather than nails on all digits except the big toe, the presence of two as opposed to three molar teeth in either side of each jaw, and by the occurrence of twin births. They eat fruits, flowers, nectar, plant exudates (gums, saps, latex) and animal prey (including frogs, snails, lizards, spiders and insects). Marmosets have morphological and behavioural adaptations for gouging trees trunks, branches and vines of certain species to stimulate the flow of gum, which they eat, and in some species form a notable component of the diet (Coimbra-Filho and Mittermeier 1976; Rylands 1984). They live in extended family groups of between four and 15 individuals. Generally, only one female per group breeds during a particular breeding season. The groups defend home ranges 10-40 ha, the size depending on availability and distribution of foods and second-growth patches.

There is no information on major threats to this species. However, it may be vulnerable because of its proximity to a number of expanding urban centres, as well as the mainstream of the Rio Amazonas, and the resulting forest destruction (Coimbra-Filho 1984). Its distribution is also cut by the Transamazônica highway (BR-230). It is probably not hunted, but there may be some use as pets.

It occurs in the Amazônia National Park (994 000 ha), Pará, where population surveys were carried out by Ayres and Milton (1981) and Branch (1983).It is listed on Appendix II of CITES (as Callithrix humeralifera).

In-Place Research, Monitoring and PlanningIn-Place Land/Water Protection and Management Conservation sites identified:Yes, over entire rangeIn-Place Species ManagementIn-Place Education Included in international legislation:Yes Subject to any international management/trade controls:Yes

1. Research -> 1.2. Population size, distribution & trends1. Research -> 1.3. Life history & ecology1. Research -> 1.5. Threats